1. Field of the Invention
The present invention relates to an electric shaver and more particularly to a rotary type electric shaver.
2. Prior Art
Electric shavers, especially rotary type electric shavers, generally include outer cutters and inner cutters; and the inner cutters are rotated on the undersurfaces of the outer cutters and cut hairs such as hairs on the head, whiskers, etc. (merely called "hairs"), which are introduced through the slits (hair entry openings) formed in the outer cutters, by a shearing force that is generated by the rotating inner cutters and the stationary outer cutters.
In today's commercially marketed electric shavers, as seen from the above, only the inner cutters, which are provided inside the head part of the shaver body, are rotated by an electric motor installed inside the shaver housing; and the outer cutters, which are also provided in the shaver head, are not rotated.
When these shavers are used, it is necessary that the hairs be introduced into the hair entry slits formed in the outer cutters; accordingly, the person using the shaver needs to constantly move the shaver head over the surface of the skin while holding the shaver housing with one hand.
However, such constant movement of the shaver during shaving while holding it with one hand over a period of several minutes to ten or so minutes causes fatigue of the arm muscles and, therefore, pain.
In view of these problems, an electric shaver that includes rotary outer cutters for smoothly bringing hairs into the hair entry slits has been proposed as disclosed in Japanese Patent Application Pre-Examination Publication (Kokai) No. H7-16360.
However, this electric shaver uses a plurality of electric motors as driving sources for rotating the outer cutter and inner cutter. Accordingly, it is difficult to construct a compact electric shaver.
Furthermore, since the outer cutter is, like the inner cutter, attached directly to the output shaft of an electric motor, the rotational speed is generally high, and this causes the skin to be abraded and injured. Furthermore, the outer cutters of electric shavers make direct contact with the skin and are therefore subjected to resistance by the skin. Thus, in order to directly drive such outer cutters, a high-torque electric motor is required However, such high-torque electric motors are generally large in size and thus conflict with the required compactness of the electric shaver. Also, such high-torque electric motors are more expensive.